1. Field of the Invention
The present invention relates generally to monitoring and controlling communications systems. More specifically, the present invention relates to a system and method for dynamic profile management in cable modem systems.
2. Related Art
Cable modems (CMs) can be found in both homes and businesses, and are used to transmit and receive digital information (e.g., to access the Internet, view television and/or on-demand video, etc.). Numerous CMs can communicate with a device known as a Cable Modem Termination System (CMTS), which is installed at a central location and used to transmit information to CMs, as well as receive information from CMs. The signal between these devices traverses a communications network that includes both coaxial cable and fiber optic cable, and is known as a Hybrid Fiber-Coax (HFC) network or cable “plant.” The protocol used to communicate between the CMTS and CMs has been standardized by the CableLabs organization and is collectively known as DOCSIS (Data Over Cable Service Interface Specifications). The set of DOCSIS specifications define all levels of communication including the physical layer, media access control layer, and an application interface layer.
FIG. 1 is a diagram depicting a typical HFC plant topology. A CMTS 102 sends data traffic and control traffic over an HFC network to CMs 110 and/or set-top boxes (STBs). The HFC network includes radio frequency (RF) amplifiers 103, fiber optic cable 104, coaxial cables 106, and fiber optic nodes 108. The HFC allows for bi-directional communication between the CMTS 102 and the CMs 110. The CMTS 102 attaches to the HFC network via coaxial cable 106. The signals being sent over the coaxial cable is then translated to fiber optic signals and then back to coax cable by the fiber nodes 108. The translation to fiber is performed in order to allow for greater distances between the CMTS and the CMs.
Typically, many CMs share the bandwidth of a single coaxial cable, which usually has a bandwidth of approximately 1 GHz. The 1 GHz spectrum is divided into multiple channels. The spectrum consumed by a given channel is defined by its center frequency and width. For example, a channel might have a center frequency of 40 MHz and a width of 6.4 MHz. The portion of the spectrum occupied by this channel is therefore defined to be from (40 MHz−6.4 MHz/2)=36.8 MHz to (100 MHz+6.4 MHz/2)=43.2 MHz. This spectrum defines a 6.4 MHz channel centered around 40 MHz.
Each defined channel is typically shared by many CMs. In the downstream direction, from the CMTS to the CM, the CMTS will use time division multiplexing to send data to all CMs using a unique address to send data to a unique CM. In the upstream direction, from the CM to the CMTS, many CMs must share the same channel. To accomplish this, the CMTS schedules time slots for each CM known as “MAPs.” A given CM is only allowed to send data during its assigned time slot. Synchronization signals from the CMTS to the CM keep the different CMs synchronized.
The HFC plant is subject to many different types of impairments that can degrade the quality of the signal. This is especially true in the upstream direction, where noise contributions from many CMs and households combine. These impairments are typically caused by problems such as loose or corroded connections, unterminated lines, faulty equipment, and other noise caused by sources such as motors and lightning. The DOCSIS specification provides a number of different tools to address the most common types of impairments such as: a variety of quadrature amplitude modulation (QAM) constellations; different channel widths; Reed-Solomon Forward Error Correction (R-S FEC); pre-equalization; and interleaving. By manually varying these parameters, a cable operator can seek to improve signal quality, making tradeoffs between throughput and improved noise immunity.
Existing CMTSs can provide various statistics which assist cable operators in determining the best configuration of settings for the CMTS given the presence of one or more impairments in a particular HFC plant. Some of these statistics include the Modulation Error Rate (MER), the percentage of correctable and uncorrectable errors, and power levels. Based upon these statistics, a cable operator can set up a configuration profile which contains the configuration parameters for the channel such as the QAM modulation order, R-S FEC codeword length and number of parity bytes, the channel width, and interleaving parameters, among other parameters.
Currently, there are some basic facilities available which allow a different upstream configuration profile to be automatically selected if certain configured thresholds are exceeded. For example, a cable operator might set up the system to move to a more robust profile if the uncorrectable error rate exceeds a certain threshold, or if the measured SNR crosses a programmed threshold. However, the process of configuring such profiles is a manual task, and typically only two different profiles are used (i.e., one primary profile and one secondary profile). In many cases, two different profiles are used because the HFC plant is noisier during certain times of the day. During these noisy periods, the CMTS can automatically switch to a different modulation profile which trades off lower performance for better noise immunity. During the quieter periods, a different modulation profile which allow for higher throughput may be used. Moreover, in the current art, the parameters within a profile are manually set up by the user, and a limited number of profiles are configured.
Typically, a single configuration profile is used for all CMs on a given channel. However, most CMTS vendors allow 2 to 4 logical channels to be configured. The logical channels all use the same physical channel. However, each logical channel may use a different profile, and CMs may be assigned to different logical channels. In this manner, some amount of customization may be achieved for different CMs on the channel.